Compositions comprising an ester compound of a polyol and a resin acid such as abietic acid (hereinafter sometimes referred to as a resin acid ester) have been widely used as tackifiers to be blended in adhesives and/or pressure-sensitive adhesives for industrial use (see, for example, Patent Literature 1). In recent years, such compositions have also been favorably used as tackifiers for medical adhesive sheets and/or pressure-sensitive adhesive sheets (e.g., patches, cataplasms, wet compresses, etc.) or for medical tapes (e.g., adhesive bandages etc.) (see, for example, Patent Literature 2).
Such adhesives and/or pressure-sensitive adhesives comprise various high molecular weight copolymers as base resins. For example, synthetic rubber elastomers such as styrene-isoprene-styrene block copolymers (SISs) and styrene-butadiene-styrene block copolymers (SBSs) have an excellent elasticity and a good adhesion to substrates and are less harmful to the human body, and therefore the copolymers have been highly consumed in the commercial market of industrial adhesives and/or pressure-sensitive adhesives, especially in the commercial market of medical adhesives and/or pressure-sensitive adhesives.
Some adhesives and/or pressure-sensitive adhesives using synthetic rubber elastomers are provided as a varnish type with an organic solvent, and others are provided as a solvent-free hot melt type in consideration of the effects on the environment and human health. Needless to say, adhesive performance such as tack is required for both types, but the hot melt type has distinctive problems as described below.
That is, synthetic rubber elastomers are highly viscid even when heated and melted at a high temperature and thus it is often difficult to use them for coating with an applicator. Accordingly, the elastomers need to be melted at a much elevated temperature for the reduction of their viscosity. However, when synthetic rubber elastomers are heated at a very high temperature, effective ingredients such as a tackifying resin blended therein may deteriorate or decompose under the heat. Further, the substrate to which hot synthetic rubber elastomers are applied may be deformed by the heat. Moreover, a large amount of electricity is required for heating the elastomers at a very high temperature, which leads to increase in the final product cost.